1. Field of the Invention
The present invention relates generally to a vehicle which has a clutch device arranged in a power transmission path between an engine and wheels, and which changes from a partial clutch engagement state to a complete connection state when the engine speed is increased to a predetermined engage rotational speed of the clutch device. In particular, the present invention is suitable for a four wheeled utility vehicle for irregular ground.
2. Description of the Prior Art
As a vehicle for running on irregular ground, there is a straddle-type all-terrain vehicle referred to as ATV and disclosed in Japanese Unexamined Patent Publication No. 11-17339, a seating-type four wheeled utility vehicle having a loading space, a straddle-type three wheeled vehicle, and an off-road motorcycle. As a clutch device mounted on the vehicles, there are a variable-speed V-belt drive having a clutch function and a centrifugal clutch device.
The vehicle for irregular ground is used for running on irregular ground such as fields, slopes, rough ground, marshes, or sandy beaches. The vehicle is therefore frequently accelerated or decelerated and started or stopped. The vehicle also often becomes stuck due to its wheel falling into a ditch or a depression.
Many riders try to get the vehicle out of the stuck state by excessively opening the throttle. Upon acceleration in the state in which the driving wheel is locked, however, in a vehicle having the variable-speed V-belt drive having a clutch function for example, the driving pulley is forcefully rotated with respect to the driven pulley in a substantially stopped state in the variable-speed V-belt drive having a clutch function. In this state, the V-belt and the driving pulley abruptly rub against each other, resulting in early wear locally caused on the V-belt. The wear locally caused on the V-belt causes the V-belt to become wavy during driving, resulting in the lowering of power transmission efficiency, whereby abnormal noise can be caused. In a vehicle having the centrifugal clutch device, burning is caused in frictional force generated sections such as a friction surface.
At present, measures for strengthening the protecting function of the clutch device of the vehicle for irregular ground are not particularly made. Such a vehicle for irregular ground is however required which protects the clutch device from the early wear on the V-belt or burning in the frictional force causing sections, and which exhibits sufficient pulling force.